The present invention relates generally to EMI/RFI shielding devices. More specifically, the invention relates to a particular EMI/RFI shielding gasket and the method of making such a gasket.
Various types of EMI/RFI gaskets are known for reducing the transmission of electromagnetic interference (EMI) and radio frequency interference (RFI). Among the known devices are gaskets having a resilient core surrounded by a deformable wire-mesh gasket material. Such gaskets are compressed around access openings and the like by the mating surfaces of a shielded housing.
Known wire-mesh gaskets are made from soft materials so that they do not break during manufacture. However, those known gaskets deflect in response to lateral pressure but do not have sufficient resiliency to restore their shape to its undeflected condition. Thus, a resilient core is relied upon to partially expand the gasket when lateral pressure is released so that the gasket can be reused. The resilient core may not fully relieve the compression set of the wire mesh because the core may also have compression set. This situation is particularly true in cyclic loading conditions. Such wire-mesh gasket materials may have a variety of cross-sectional shapes such round, rectangular, double cores, and round having a fin. Suitable known materials are tin-plated phosphor bronze, tin-coated copper-clad steel, silver-plated brass, monel, and aluminum. A variety of such wire-mesh gaskets are made by Tecknit EMI Shielding Products. Different core cross sections and materials are used for different applications.
Other types of gaskets are also known which are fashioned from heat-treated beryllium copper. Such gaskets typically include similarly shaped elements sequentially arranged, e.g., longitudinally along a strip. Heat-treated beryllium copper is used because of its resilience and due to its excellent electrical conductivity. Heat-treated or cold-worked beryllium copper has limited elongation and is subject to breakage when subjected to small radius bends associated with knitting and braiding processes. Accordingly, beryllium copper has not been suitable for use in knitted and braided applications like those used for wire-mesh gasket construction.